1. Field of the Invention
The present disclosure relates to graphic image data compression, and more particularly, to graphic image data compressors using an effective loss compression algorithm in a system with a restricted bandwidth, and a method of compressing graphic image data.
2. Description of the Related Art
Digital broadcasting is distinguished from analog broadcasting in that relatively numerous types of services can be provided to users. Users expect the digital broadcasting to provide pictures with good quality. Since a receiver performs a variety of functions including a display of graphic image data, the graphic image data have restricted bandwidths.
Digital broadcasting data may be stored in a memory included in the receiver and transmitted to necessary function blocks by a controller using ground waves. Graphic image data included in the ground waves are stored in the memory and transmitted by the controller to a display device, such as a monitor. Among various service function blocks of the receiver, function blocks used to process graphic image data relevant to the present disclosure will now be described.
FIG. 1 is a block diagram illustrating a digital receiver for processing graphic image data. Referring to FIG. 1, the digital receiver 100 includes a CPU 110, a graphic processor 120, a memory 130, a display processor 140, and a monitor 150. Graphic image data are transmitted to the function blocks of the digital receiver 100 through a bus embedded therein.
The graphic processor 120 transmits graphic image data to the memory 130 through the bus under the control of the CPU 110. The display processor 140 transmits the graphic image data stored in the memory 130 to the monitor 150 through the bus. The monitor 150 displays the graphic image data.
Each data of various services performed by the digital receiver has a restricted bandwidth. Graphic image data also have restricted bandwidths. Since more graphic image data are processed than service data, graphic image data are compressed and stored in the memory.
FIG. 2 is a block diagram illustrating a conventional digital receiver for compressing and storing graphic image data. Referring to FIG. 2, the digital receiver 200 includes a CPU 210, a graphic processor 220, a compressor 230, a memory 240, a de-compressor 250, a display processor 260, and a monitor 270. Since the digital receiver 200 additionally includes the compressor 230 and the de-compressor 250 as compared with the digital receiver 100 shown in FIG. 1, the compressor 230 and the de-compressor 250 will now be described.
The compressor 230 compresses graphic image data received from the graphic processor 220 to a smaller data stream using a predetermined algorithm and stores the compressed data in the memory 240 through a bus. The de-compressor 250 decompresses the compressed data read from the memory 240 and transmits the decompressed data to the monitor 270 to display the data.
A process of compressing and decompressing graphic image data may cause a loss of compressed data. To avoid such loss, lossless compression methods such as Run Length Encoding (RLE) and Differential Pulse Code Modulation (DPCM) are widely used. Here, a loss compression method can be used for a system capable of dealing with the data loss in order to equally process other data.
Graphic image data typically have different compression rates according to the kinds of graphic images. A graphic image with little change can have a very high compression rate, while a compressed graphic image with many changes may be larger than an uncompressed graphic image.
A data bandwidth between the memory 240 and the display processor 260 becomes much narrower due to a data bit width of the memory 240 and an operation frequency of the digital receiver providing various kinds of services. In this case, graphic image data must be compressed with a high compression rate to satisfy its bandwidth. If compression fails, conventional image pixel data may be repeatedly displayed or a current image may be skipped.